Search Results (727)

Petrological knowledge on weathering processes controlling the mobility of chemical elements is still limited in the dry tropical zone of Cameroon. This study aims to investigate the mobility of major and trace elements during rhyolite weathering and soil formation in Mobono by understanding the mineralogical and elemental vertical variation. The studied soil was classified as Cambisols containing mainly quartz, K-feldspar, plagioclase, smectite, kaolinite, illite, calcite, lepidocrocite, goethite, sepiolite, and interstratified clay minerals. pH values ranging between 6.11 and 8.77 indicated that hydrolysis, superimposed on oxidation and carbonation, is the main process responsible for the formation of secondary minerals, leading to the formation of iron oxides and calcite. The bedrock was mainly constituted of SiO₂, Al₂O₃, Na₂O, Fe₂O₃, Ba, Zr, Sr, Y, Ga, and Rb. Ce and Eu anomalies, and chondrite-normalized La/Yb ratios were 0.98, 0.67, and 2.86, respectively. SiO₂, Al₂O₃, Fe₂O₃, Na₂O, and K₂O were major elements in soil horizons. Trace elements revealed high levels of Ba (385 to 1320 mg kg⁻¹), Zr (158 to 429 mg kg⁻¹), Zn (61 to 151 mg kg⁻¹), Sr (62 to 243 mg kg⁻¹), Y (55 to 81 mg kg⁻¹), Rb (1102 to 58 mg kg⁻¹), and Ga (17.70 to 35 mg kg⁻¹). LREEs were more abundant than HREEs, with LREE/HREE ratio ranging between 2.60 and 6.24. Ce and Eu anomalies ranged from 1.08 to 1.21 and 0.58 to 1.24 respectively. The rhyolite-normalized La/Yb ratios varied between 0.56 and 0.96. Mass balance revealed the depletion of Si, Ca, Na, Mn, Sr, Ta, W, U, La, Ce, Pr, Nd, Sm, Gd and Lu, and the accumulation of Al, Fe, K, Mg, P, Sc, V, Co, Ni, Cu, Zn, Ga, Ge, Rb, Y, Zr, Nb, Cs, Ba, Hf, Pb, Th, Eu, Tb, Dy, Ho, Er, Tm and Yb during weathering along the soil profile. Full article

This study synthesized FeNiCuAlX high-entropy alloys (HEAs) (where X = Cr, Co, Mn) using arc melting and investigated their high-temperature oxidation behavior in air at 900 °C. The oxidation kinetics of all alloys followed a parabolic rate, with the oxidation rate constants (kp) of FeNiCuAlCr, FeNiCuAlCo, and FeNiCuAlMn being approximately two to three orders of magnitude lower than that of the FeNiCu alloy. Specifically, FeNiCuAlCr exhibited the lowest kp value of 1.72 × 10⁻⁶ mg²·cm⁴/s, which is significantly lower than those of FeNiCuAlCo (3.29 × 10⁻⁶ mg²·cm⁴/s) and FeNiCuAlMn (1.71 × 10⁻⁵ mg²·cm⁴/s). This suggests that the addition of chromium promotes the formation of a dense Al₂O₃/Cr₂O₃ oxide layer, significantly enhancing the oxidation resistance. Furthermore, corrosion resistance was assessed through potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution. FeNiCuAlCr demonstrated exceptional resistance to localized corrosion, as indicated by its low corrosion current density (45.7 μA/cm²) and high pitting potential (−0.21 V), highlighting its superior corrosion performance. Full article

The development of anode-free sodium metal batteries (AFSMBs) offers a promising pathway to achieve ultrahigh energy density and cost efficiency inherent to conventional sodium ion/metal batteries. However, irreversible Na plating/stripping and dendritic growth remain critical barriers. Herein, we demonstrate that separator engineering is a pivotal strategy for stabilizing AFSMBs. Through systematic evaluation of four separators—2500 separator (PP), 2325 separator (PP/PE/PP), glass fiber (GF), and an Al₂O₃-coated PE membrane, we reveal that the Al₂O₃-coated separator uniquely enables exceptional interfacial kinetics and morphological control. Na||Na symmetric cells with Al₂O₃ coated separator exhibit ultralow polarization (4.5 mV) and the highest exchange current density (1.77 × 10⁻² mA cm⁻²), while the anode-free AlC-NFPP full cells retain 91.6% capacity after 150 cycles at 2C. Specifically, the Al₂O₃ coating homogenizes Na⁺ flux, promotes dense and planar Na deposition, and facilitates near-complete stripping with minimal “dead Na”. This work establishes ceramic-functionalized separators as essential enablers of practical high-energy AFSMBs. Full article

This study evaluated the inhibitory efficacy of sulphur dioxide, hydrogen peroxide, copper sulphate pentahydrate, chlorine-based formulations, a chlorine-free formulation, ethanol, and acetic acid against Cladosporium cladosporioides, Aspergillus niger, and Penicillium expansum. An in vitro inhibition test was employed to investigate the inhibitory properties. The results demonstrated different sensitivities of filamentous fungi to the inhibitors. All tested substances displayed fungicidal properties. Sulphur dioxide (40% NH₄HSO₃ solution) inhibited growth at a 4% v/v concentration. No minimum effective concentration was established for H₂O₂; only a 30% w/v solution inhibited P. expansum. CuSO₄·5H₂O completely inhibited fungal growth at 5% w/v solution, with 2.5% w/v also proving effective. For the chlorine-based product, 40% w/v solution (48 g∙L⁻¹ active chlorine) had the most substantial effect, though it only slowed growth, and NaClO solution completely inhibited growth at 2.35 g NaClO per 100 g of product (50% w/v solution). FungiSAN demonstrated fungicidal effects; however, the recommended dose was insufficient for complete inhibition. Ethanol exhibited the lowest efficacy, while the inhibitory threshold for CH₃COOH was found to be a 5% v/v solution. The findings of this study may serve as a basis for informed decision-making when selecting the most suitable product, depending on specific application conditions. Full article

This study explored the potential of chitosan (CH)/bacterial cellulose (BC) complexes (0.5% w/v) as novel emulsifiers to stabilize oil-in-water (o/w) Pickering emulsions (20% v/v sunflower oil), with a focus on their gel-like behavior. Emulsions were prepared using CH combined with BNC derived via H₂SO₄ (BNC1) or H₂SO₄-HCl (BNC2) hydrolysis. Increasing BNC content improved stability by reducing phase separation and enhancing viscosity, while CH contributed interfacial activity and electrostatic stabilization. CH/BNC1_25:75 emulsions showed the highest stability, maintaining an emulsion stability index (ESI) of up to 100% after 3 days, with minimal change in droplet size (R_h ~8.5–8.8 μm) and a positive ζ-potential (15.1–29.8 mV), as confirmed by dynamic/electrophoretic light scattering. pH adjustment to 4 and 10 had little effect on their ESI, while ionic strength studies showed that 0.1 M NaCl caused only a slight increase in droplet size combined with the highest ζ-potential (−35.2 mV). Higher salt concentrations led to coalescence and disruption of their gel-like structure. Rheological analysis of CH/BNC1_25:75 emulsions revealed shear-thinning behavior and dominant elastic properties (G′ > G″), indicating a soft gel network. Incorporating sunflower-seed protein isolates into CH/BNC1 (25:75) emulsions led to coacervate formation (three-layer system), characterized by a decrease in droplet size and an increase in ζ-potential (up to 32.8 mV) over 7 days. These findings highlight CH/BNC complexes as sustainable stabilizers for food-grade Pickering emulsions, supporting the development of biopolymer-based emulsifiers aligned with bioeconomy principles. Full article

This study investigates the microstructural evolution, mechanical behavior, and electrochemical performance of CoCrFeNiNb and CoCrFeNiV HEAs fabricated via mechanical alloying and spark plasma sintering. Microstructural analyses reveal that the alloys have a face-centered cubic (FCC) matrix with Nb-enriched Laves and V-enriched σ phases. The CoCrFeNiNb HEA exhibits superior compressive strength and hardness than CoCrFeNiV due to uniform Laves phases distribution. Fracture surface analysis reveals that at lower sintering temperatures, the fracture is primarily caused by incomplete particle bonding, whereas at higher temperatures, brittle fracture modes dominated via transgranular cracking become predominant. The research results of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) show that both alloys exhibited superior electrochemical stability in a 3.5 wt.% NaCl solution compared to the CoCrFeNi base alloy. X-ray photoelectron spectroscopy (XPS) analysis confirms the formation of stable oxide layers (Nb₂O₅ and V₂O₃) on the precipitated phases, acting as protective barriers against chloride ion penetration. The selective oxidation of Nb and V improves the integrity of the passive film, reducing the corrosion rates and enhancing the long-term durability. These findings highlight the critical role of precipitated phases in enhancing the corrosion resistance of HEAs, and emphasize their potential for use in extreme environments. Full article

Air stability caused by the H₂O/CO₂ reaction at the layered oxide NaTMO₂ surface is one of the main obstacles to commercializing sodium-ion batteries (SIBS). The H₂O and CO₂ adsorption properties on the (100) surface of sodium layered transition metal oxide NaTMO₂ (TM = Co, Ni, Mo, Nd) are calculated using the DFT method to study the surface air stability. This study showed that the material bulk phase (symmetry), surface site, element type, and surface termination are all (though not the only) important factors that affect the adsorption strength. Contrary to previous studies, the P phase is not always more air-stable than the O phase; our calculations showed that the NaNiO₂ O phase is more stable than the P phase. The calculated band center and occupation showed a direct relationship with the adsorption energy. The Na site adsorption for CO₂ and H₂O showed the same V-shape trend. However, the TM adsorption for CO₂ and H₂O showed a different trend. With an increased t₂g band center, CO₂ adsorption strength increases. There is no clear trend for H₂O adsorption. Our calculations showed that the electronic structure of the surface atomic of adsorption site plays a decisive role in CO₂ and H₂O adsorption strength. This study demonstrated an effective method for obtaining a stability parameter regarding the electronic structure, which can be used to screen the air-stable layered oxide sodium cathode in the future. Full article

Na₀.₈₉Co_0.90Me_0.10O₂ (Me = Cr, Ni, Mo, W, Pb, and Bi) ceramic samples were prepared using a solid-state reaction method, and their crystal structure, microstructure, and electrical, thermal, and thermoelectric properties were investigated. The effect of the nature of the doping metal (Me = Cr, Ni, Mo, W, and Bi) on the structure and properties of layered sodium cobaltite Na_0.89CoO₂ was analyzed. The largest Seebeck coefficient (616 μV/K at 1073 K) and figure-of-merit (1.74 at 1073 K) values among the samples studied were demonstrated by the Na_0.89Co_0.9Bi_0.1O₂ solid solution, which was also characterized by the lowest value of the dimensionless relative self-compatibility factor of about 8% within the 673–873 K temperature range. The obtained results demonstrate that doping of layered sodium cobaltite by transition and heavy metal oxides improves its microstructure and thermoelectric properties, which shows the prospectiveness of the used doping strategy for the development of new thermoelectric oxides with enhanced thermoelectric characteristics. It was also shown that samples with a higher sodium content (Na:Co = 0.89:1) possessed higher chemical and thermal stability than those with a lower sodium content (Na:Co = 0.55:1), which makes them more suitable for practical applications. Full article

A SiO₂-Al₂O₃-B₂O₃-CaO-MgO-Na₂O glass-based protective lubricant coating was developed for Ti-6Al-4V alloy forging, featuring a fully non-toxic formulation. The coating consisted of a composite glass matrix formed by blending two phases with distinct softening temperatures, extending its operational window to 700–950 °C. The composite glass showed initial softening at 700 °C and complete melting at 800 °C, with contact angle measurements confirming superior wettability (θ < 90°) across the forging range (800~950 °C). With an increase in temperature, the surface tension of the composite glass melt decreased, and subsequently, the wettability of the composite glass melt was significantly improved. XRD revealed that the uncoated Ti-6Al-4V formed a 22 μm thick rutile TiO₂ scale with a porous structure and interfacial cracks, while the coated sample retained an amorphous glass layer with no TiO₂. Cross-sectional SEM showed a crack-free, poreless interface with strong metallurgical bonding, in contrast to the uncoated sample’s spalled oxide layer. EDS showed minimal oxygen diffusion of the glass coating into the substrate. Ring upsetting tests showed that the coating reduced friction from 0.5–0.7 to 0.3 (50–57% decrease). Collectively, the glass protective lubricant coating showed good performance in terms of protection and lubrication. Full article

The new mineral achyrophanite (K,Na)₃(Fe³⁺,Ti,Al,Mg)₅O₂(AsO₄)₅ was found in high-temperature sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite-group sulfates, hematite, alluaudite-group arsenates (badalovite, calciojohillerite, johillerite, nickenichite, hatertite, and khrenovite), ozerovaite, pansnerite, arsenatrotitanite, yurmarinite, svabite, tilasite, katiarsite, yurgensonite, As-bearing sanidine, anhydrite, rutile, cassiterite, and pseudobrookite. Achyrophanite occurs as long-prismatic to acicular or, rarer, tabular crystals up to 0.02 × 0.2 × 1.5 mm, which form parallel, radiating, bush-like, or chaotic aggregates up to 3 mm across. It is transparent, straw-yellow to golden yellow, with strong vitreous luster. The mineral is brittle, with (001) perfect cleavage. D_calc is 3.814 g cm^–3. Achyrophanite is optically biaxial (+), α = 1.823(7), β = 1.840(7), γ = 1.895(7) (589 nm), 2V (meas.) = 60(10)°. Chemical composition (wt.%, electron microprobe) is: Na₂O 3.68, K₂O 9.32, CaO 0.38, MgO 1.37, MnO 0.08, CuO 0.82, ZnO 0.48, Al₂O₃ 2.09, Fe₂O₃ 20.42, SiO₂ 0.12, TiO₂ 7.35, P₂O₅ 0.14, V₂O₅ 0.33, As₂O₅ 51.88, SO₃ 1.04, and total 99.40. The empirical formula calculated based on 22 O apfu is Na_1.29K_2.15Ca_0.07Mg_0.34Mn_0.01Cu_0.11Zn_0.06Al_0.44Fe³⁺_2.77Ti_1.00Si_0.02P_0.02S_0.14V_0.04As_4.90O₂₂. Achyrophanite is orthorhombic, space group P222₁, a = 6.5824(2), b = 13.2488(4), c = 10.7613(3) Å, V = 938.48(5) ų and Z = 2. The strongest reflections of the PXRD pattern [d,Å(I)(hkl)] are 5.615(59)(101), 4.174(42)(022), 3.669(31)(130), 3.148(33)(103), 2.852(43)(141), 2.814(100)(042, 202), 2.689(29)(004), and 2.237(28)(152). The crystal structure of achyrophanite (solved from single-crystal XRD data, R = 4.47%) is unique. It is based on the octahedral-tetrahedral M-T-O pseudo-framework (M = Fe³⁺ with admixed Ti, Al, Mg, Na; T = As⁵⁺). Large-cation A sites (A = K, Na) are located in the channels of the pseudo-framework. The achyrophanite structure can be described as stuffed, with the defect heteropolyhedral pseudo-framework derivative of the orthorhombic Fe³⁺AsO₄ archetype. The mineral is named from the Greek άχυρον, straw, and φαίνομαι, to appear, in allusion to its typical straw-yellow color and long prismatic habit of crystals. Full article

Ceramic oxide coatings were fabricated on 7075 aluminum alloy via micro-arc oxidation (MAO) in a silicate-phosphate electrolyte under voltages of 250 V, 300 V, and 350 V for 600 s. The effect of the applied voltage on the surface morphology, microstructure, phase composition, microhardness, roughness, coating thickness, and corrosion resistance was systematically studied. The coating obtained at 300 V demonstrated a dense structure with relatively low surface roughness (2.3 μm) and a thickness of approximately 70 μm. This sample also exhibited the most balanced performance, combining relatively high microhardness (~422 HV) and the lowest corrosion current density (6.1 × 10⁻⁷ A/cm²) in a 3.5 wt.% NaCl solution. X-ray diffraction patterns revealed the presence of both γ- and α-Al₂O₃ phases in all coated samples, with a relative increase in α-phase intensity observed at an intermediate voltage. The results demonstrate that the applied voltage plays a critical role in determining the coating structure and performance, offering insights into the surface treatment of high-strength aluminum alloys for engineering applications. Full article

Composite electrodeposited coatings hold significant potential for marine and aerospace applications due to their synergistic corrosion resistance and wear durability, yet nanoparticle agglomeration and interfacial incompatibility persistently undermine their performance. Conventional dispersion techniques—mechanical agitation, surfactants, or high-energy methods—fail to resolve these issues, often introducing residual stresses, organic impurities, or thermal damage to substrates. This study addresses these challenges through a novel thermal-assisted alkaline etching (TAE) protocol that synergistically removes surface oxides and enhances colloidal stability in β-SiC nanoparticles. By combining NaOH-based etching with low-temperature calcination (250 °C), the method achieves oxide-free SiC surfaces with elevated hydrophilicity and a ζ-potential of −25 mV, enabling submicron clustering (300 nm) without surfactants. Electrodeposited Co/SiC coatings incorporating TAE-SiC exhibited current-modulated reinforcement, achieving optimal SiC incorporation (5.9 at% Si) at 8 A/dm² through electrophoretic–hydraulic synergy, along with uniform cross-sectional distribution validated by SEM. Tribological assessments revealed shorter wear tracks in TAE-SiC-enhanced coatings compared to their untreated counterparts, suggesting enhanced interfacial coherence despite a comparable mass loss. Demonstrating scalability through cost-effective aqueous-phase chemistry, this methodology provides a generalized framework applicable to other ceramic-reinforced systems (e.g., Al₂O₃ and TiC), offering transformative potential for next-generation protective coatings in harsh operational environments. Full article

Inorganic arsenic [As(III) and As(V)] is a pervasive environmental contaminant in groundwater systems, early-life exposure to which is associated with an impaired cognitive ability and an increased risk of neurobehavioral disorders. Although the effect of As(III) on the neurons is well studied, the involvement of the microglia remains unclear. In this study, the effects of sodium arsenite (NaAsO₂) on microglial activation and the underlying NLRP3 inflammasome mechanism were determined. Pregnant rats were gavaged with NaAsO₂ (0, 1, 4, and 10 mg/kg body weight), which dissociates in aqueous solutions into bioactive arsenite species [As(OH)₃], from gestational day 1 (GD1) to postnatal day 21 (PND21). The results showed that As(III) induces learning and memory impairments and microglial activation in the hippocampus of offspring rats (PND21). Increased expression of NLRP3, the activation of caspase-1, and the production of interleukin-1β were observed in both the hippocampus of As(III)-exposed offspring rats and As(III)-exposed microglial BV2 cells under culture conditions. Interestingly, blocking the NLRP3 inflammasome using MCC950 mitigated its activation. Furthermore, inhibition of NADPH oxidase 2 (NOX2) using apocynin or specific siRNA significantly reduced As(III)-induced microglial NLRP3 inflammasome activation. In addition, inactivation of the microglial NLRP3 inflammasome or NOX2 markedly rescued As(III)-induced neurotoxicity in the hippocampal HT22 cells. Taken together, this study reveals that NOX2/NLRP3-inflammasome-dependent microglial activation promotes As(III)-induced learning and memory impairments in developmental rats. Full article

2,5-Furandicarboxylic acid (FDCA) is a bio-based platform chemical with high potential to replace terephthalic acid in polymer production, particularly for polyethylene furanoate (PEF), a biopolymer with superior thermal and barrier properties. This study investigates the selective oxidation of 5-hydroxymethylfurfural (HMF) into FDCA using nickel-based heterogeneous catalysts, aiming at a cost-effective and sustainable alternative to noble metal catalysts. A series of nickel oxide catalysts were synthesized and screened. The NiOx catalyst synthesized without thermal treatment via Route B showed the best performance, achieving a FDCA yield of 11.77%, selectivity of 27.41%, and concentration of 0.9 g/L under preliminary conditions. Reaction kinetics revealed that the controlled addition of NaClO enhanced FDCA yield by 2.28 times. Optimization using a 2³ factorial design identified the optimal conditions as 6% (w/v) catalyst concentration, 25 °C, and a NaClO:HMF molar ratio of 12:1, leading to 34.14% yield and 42.57% selectivity. The NiOx catalyst maintained its activity over five successive cycles, indicating good recyclability. Moreover, NiOx demonstrated catalytic activity with crude HMF derived from glucose dehydration, confirming its practical applicability. These results support the potential of nickel-based catalysts in sustainable FDCA production, contributing to the advancement of bio-based polymer synthesis. Full article

To enhance the signal intensity of kynurenines, which are present at trace concentrations in biological fluids, a novel analytical approach was developed, combining pressure-assisted electrokinetic injection (PAEKI) with a mixed micelle system based on sodium dodecyl sulfate (SDS) and Brij-35. The method was applied to key compounds of the kynurenine pathway, including L-tryptophan, kynurenine, 3-hydroxykynurenine, and kynurenic acid, as well as to the aromatic amino acids (AAs) L-tyrosine and L-phenylalanine. PAEKI was performed by electrokinetic injection for 2 min at −6.5 kV (reversed polarity) and 0.5 psi (3.45 kPa) using a fused silica capillary (50 cm in length, 50 µm inner diameter). The background electrolyte (BGE) consisted of 20 mM Na₂B₄O₇ (pH 9.2), 2 mM Brij-35, 20 mM SDS, and 20% (v/v) methanol (MeOH). The limit of detection (LOD) using a diode array detector (DAD) was 1.2 ng/mL for kynurenine and ranged from 1.5 to 3.0 ng/mL for the other analytes. The application of PAEKI in conjunction with micellar electrokinetic capillary chromatography (MEKC) and solid-phase extraction (SPE) of artificial urine samples resulted in a 146-fold increase in signal intensity for kynurenines compared to that observed using the hydrodynamic injection (HDI) mode. The developed method demonstrates strong potential for determining kynurenine pathway metabolites in complex biological matrices. Full article